The Angel of the LORD
"I suspect the Angel of the LORD is Jesus before his incarnation:
John 1:18 (NIV) No one has ever seen God, but God the One and Only, who is at the Father's side, has made him known.
Joshua 5:13-15 (NIV) The commander of the LORD's army replied, "Take off your sandals, for the place where you are standing is holy." And Joshua did so.